Film production generally employs a blowing method or a casting method. The starting material is a plastic granulate that has graded properties, but has characteristics that differ from one batch to the next. In addition, the raw material can differ in temperature, moisture content, and aging. Differences in the material, especially the molecular structure, can result in different development of sensible heat in a worm conveyer screw of the extruder, which also influences the result. It is known that a conditioner located between the raw material silo and the extruder can adjust the state of the material suitably for the process.
The actual formation or crystallization then takes place after extrusion when the plastic is already in the film form, during the cooling and hardening of the film.
The quality of the film that is eventually obtained is evidenced by freedom from pinholes, in other words inclusions such as gel bodies, foreign matter, and burned plastic deposits, for example, as well as by the material and thickness homogeneity of the film and its uniform transparency, which has been shown to be an indicator of morphological structure. According to the prior art, when film sections that cannot be used are produced, they are destroyed and an attempt is made to adjust the parameters at the extruder.
However, correction of the factors that influence the quality of the film turns out to be rather complex. Accordingly, it has not yet been possible to perform continuous real-time control of the properties of such films.